Toroidal apparatus with winding surrounding both core and gap wherein permeable material is variably positioned



y 27, 1965 s. E. BOGOTCH ETAL 3, 7,721

TOROIDAL APPARATUS WITH WINDING SURROUNDING BOTH CORE AND GAP WHEREIN PERMEABLE MATERIAL IS VARIABLY POSITIONED Filed July 1, 1963 2 Sheets-Sheet 1 m/ I h I \M [6 1:

INVENTORS STANLEY E. BOGOTCH ROBE/77' R lNGRAM V/CTOI? 6. ZOUR/DES' ATTORNEY July 27, 1965 s. E. BOGOTCH ETAL 3,197,721 TOROIDAL APPARATUS WITH WINDING SURROUNDING BOTH CORE AND GAP WHEREIN PERMEABLE MATERIAL IS VARIABLY POSITIONED Filed July 1, 1963 2 Sheets-Sheet 2 FIG. 3a. FIG.3b.

F|G .3c.

F| G.4d. FlG.4b.

INVENTORS STANLEY E BOGOTCH ROBERT R /NGRAM United States Patent Ofiice ilhiifi l Patented July 27, 1955 TGROIDAL APPARATUS WITH WTNDENG SUP- RUUNDKNG EGTH CQRE AND GAP WHEREEN PERMEABLE MATERIAL IS VARIABLY PGJSI- TIBNED Staniey E. Bogotch, Forest Hills, Robert R. Ingram, Commaclt, and Victor G. Zourides, Brooklyn, I' LY assignors to Sperry Rand Corporation, Great Neck, N.Y., a corporation of Delaware Filed July 1, 1963, Ser. No. 2%,644 7 Claims. (Cl. 333-75) This invention relates in general to inductors and more particularly to a toroidally wound inductor that may be tuned to change its inductance by as much as forty percent. Such an inductor is provided (1) by slotting a closed loop of permeable material and providing a permeable slug positionable within the slot and (2) by so winding a coil of wire on the permeable loop that turns of wire pass through the slot provided, the ends of the coil wire not being immediately adjacent the slot.

The prior art is replete with tunable inductors having permeable slugs positionable relative to coils, such inductors being usually solenoidal in nature. However, solenoids have the disadvantage of not being able to confine their induced magnetic fields and thereby often electrically interfere with other components in the circuits in which they are used. T oroidally wound cores contrarily confine their induced magnetic fields to within their respective core materials, but because of this have been heretofore considered substantially untunable, i.e. merely slotting a loop of permeable material between the two ends of a supported toroidal winding, while providing a positionable slug for such slot, results in a change in coil inductance of only about 1% when such slug is moved in and out of the slot. An explanation for this occurrence is as follows: With the slug totally out of the slot, only a relatively small amount of flux bridges the slot and links all turns of the coil (small inductance), the rest leaking back to link only some coil turns; with the slug totally in the slot, small air gaps between the slug and the toroidal core still exist, with substantial leakage being still prevalent.

Following are two compatible theories of why the technique of winding and slotting, as taught by the present invention, provides a substantial change in inductance as a slug is moved from a position totally without a core slot to a position totally within the slot:

Theory I.A winding in the slot hinders flux leakage when the slug is totally out of the slot (providing therefore a slightly higher minimum inductance level than is obtained for an equivalent toroidal core slotted between the coil ends) and virtually prevents flux leakage when the slug is in the slot, i.e. the winding in the slot directs the flux (which ordinarily would leak out of the slot) through the slug so that practically all of the flux created by the winding links all of the winding turns, providing therefore a substantially high inductance. As a side ad vantage, and in accord with this theory, is the fact that a toroidal core slotted per the invention permits flux leakage (between the winding ends) in an area where the tendency for such leakage is low.

Theory lI.--By acting to drive flux deliberately through the slug, its permeability (and hence the overall permeability of the slot area) is directly affected when the slug is moved in and out of the slot, i.e. the permeability of a medium is generally increased when the flux in the medium is increased. With the slug totally out of the slot, the inductance of the toroidal winding is relatively slight due to leakage as heretofore mentioned; but with the slug totally in the slot, the permeability of the slot area greatly increases, providing therefore substantially increased flux to link the coil, i.e. increased inductance for the coil.

A principal object of the invention is to provide a tunable inductor having a substantial tuning range.

Another object of the invention is to provide a tunable substantially toroidally wound inductor wherein the winding thereof is caused to extend through a slot provided in a winding-supporting core.

Another object of the invention is to provide a tunable all-pass network wherein tunable substantially toroidally wound inductors are employed, such network being easily tuned for particular frequency, impedance, and phase shift with frequency characteristics.

The invention will be described with reference to the figures wherein:

FIGS. 1a and 1b show respectively plan and side views of one form of the invention,

FIGS. 2a and 212 show respectively plan and side views of a second form of the invention,

FIG. 3a, 3b and 3c are views or" still another form of the invention,

FIGS. 4a and 4b are depictions of a presently preferred storm of the invention, and

FIG. 5 is a schematic diagram of an all-pass filter improved by the present invention.

Referring to FIGS. 1a and 1b a ring 19 of permeable material is slotted at 12 and has a continuous winding 14 supported thereon. The ring 10 is fixedly held in a recess 16 in a block 18 of nonmagnetic material. The winding 14 is brought in and started at a place which is approximately diametric to the slot 12, which of course causes the winding (being continuous) to extend through and around part of the slot. A channel 26 in the block 18 serves as a guide for a slug 22 of permeable material, such slug 22 being movable into and out or" the slot 12 by means of a screw 24. The screw 24 may be driven along the axis of the slot by a nut 26 positioned on one side of an immovable support 28 (fixed to the block 18) and held there by a lock washer 30 located on the other side of the support 28. Both the slug Z2 and the slot 12 are similarly tapered to fit together snugly when the slug is all the way in its slot.

In operation, the nut 26 is turned in one direction to move the slug 22 into the slot 12 to increase the inductance of the winding 14; by turning the nut 26 in an opposite direction the slug 22 is removed from the slot 12 to d crease the winding inductance.

Referring to FIGS. 2a and 212, two semirounds 32 and 34 of permeable material are embedded respectively in recesses 36 and 38, the recesses being respectively in fixed and positional members 5%]! and 42. The semiround 32 has a winding 44 brought in and started at 46. The winding 44 extends clockwise from the semiround 32 to bridge an air gap 48 between the semirounds, being continued on and supported by the semiround 34 only to bridge again an air gap 5% and wind up being completed on the semiround 32 at The positionable member 4-2 is adapted to be slid along a face 52 on the fixed member 4%; by means of a screw 54- rotatably mounted in a sup port 56, i.e. by rotating a knob 53 the screw 54 is made to turn to move the member 42 closer to or farther from the member 4a, thereby closing or opening the gaps 48 and 5t? simultaneously (to increase or decrease the inductance of the winding 44). To be noted with particularity is the cast that in this form of the invention the winding 44 extends across and surrounds two air gaps (4S and Eli).

Referring to FIGS, 3a, 3b and 30, a form of the invention is shown which provides for tuning an inductor according to the invention by moving a tuning slug not perpendicular to, but parallel to the axis of a substantially toroidally wound core. A ring 51 of permeable material, supporting a toroidal winding 53, is provlded W a triangular slot 55 across which the wmdrn 53 eiitellds and surrounds part thereof. The ring 51 and wind ng 53 are immovably encased in a receptacle 57 in a housing 59 made of nonmagnetic material. The slot 55 is adapted to retain a positionable slug 61 made from permeable material, such slug 61 being tapered to be capa l Of forming a tight fit with the sides of the slot 55. A stem 63, preferably of nonmagnetic material, secured to the slug 61 is adapted to move the slug translationally lnto and out of its receiving slot 55. A set screw 65 is provided to hold the slug 61 immovable once the inductance of the coil 53 is set for a given amount, the stem 63 being slidable within an opening 67 in the housing 59.

In FIGS. 4a and 4b, a presently preferred form of the invention is shown, such form being presently preferred because of its neat integral package. A ring of permeable material 60 supports a winding 62 substantially toroidally wound on the ring 60. A triangularly shaped slot 64 is provided on the ring 69 and the winding 62 is so aranged and wound on the ring that turns thereof surrounds the gap 64-. A permeable slug 66, tapered at 68 to provide a tight fit with the sides of the slot 64, has a stem 7% adapted to be positionably held within an internal sleeve 72. The winding 62. in the vicinity of the slot 64 is so arranged that movement of the slug 66 and its stem are not interfered with, i.e. the winding in the vicinity of the slot appears wound around the stem when the stem 70 is in its sleeve. The stem 70 is preferably of nonmagnetic material, being provided with a set screw 74 that bears against the stem 70 to prevent movement of the slug 66 once the slug is properly placed in its slot. The winding 62 is started and terminated substantially opposite the slot 64, and the entire assembly described above is encapsulated in a nonmagnetic material 100, preferably plastic.

The pronounced need for tunable toroidal-type inductors has ben brought about by the advent of pulse compression radars of the type described in C. E. Cook, Modification of Pulse Compression Waveforms, Na- .tional Electronics Conference Proceedings, vol. 14 (October 1958), pp. 1058-1067. In such radars, networks are oftentimes needed to compress frequency modulated target echo signals by time delay-as-a-function-of-signal frequency techniques. As has been the practice, these networks usually are of a bridged T form, e.g. a parallel tuned circuit with split capacitors and a series tuned circuit connected to the parallel tuned circuit at the junction of the split capacitors. Both tuned circuits must be tuned to the same frequency if the network is to have all-pass qualities. This means that the L and C (inductance and capacitance) products for the two tuned circuits must be identical. In addition, because each such network is but a small part of an overall system, consideration must be given to network characteristic impedance for matching purposes). That is, the ratio of the inductance in the parallel tuned circuit of a given network to the capacitance between such circuit and ground must be known, such ratio being also required to be known since it bears directly on the degree of signal time delay with frequency.

In the past, fixed and extremely accurate inductors have been employed in both the parallel and series tuned circuits of the above-mentioned networks, the variable elements in these networks being solely capacitors. With fixed accurate inductors, the capacitors are varied for frequency considerations, immediately making the L and C product and ratio values, and the exact value of each inductance the capacitance, known. However, because of the extreme expense of highly accurate inductors, the networks in question have become excessively costly, i.e. in a given radar, literally hundreds of these networks are employed.

Since fixed inexpensive capacitors are readily available to within extremely close tolerances, the present invention proposes the use of these with the aforedescribed tunable inductors in bridged T all-pass networks. Then, inductance tuning of these networks for frequency response will result in readily ascertainable inductance values, from which impedance and time delay characteristics can be easily determined.

Referring to FIG. 5, a bridged T circult consists of a parallel tuned circuit 30 and a series tuned circuit 82. The parallel tuned circuit comprises an inductor 83, e.g. one of the types shown in FIGS. 1a through 4b, connected across highly accurate split capacitors 34 and 86. A tunable inductor 88 together with a highly accurate capacitor 9% comprises the series tuned circuit 82. Adjustment of the inductor 33 for a given resonant frequency for the circuit 80, followed by ad ustment of the inductor S8 to provide the circuit 82 with that same resonant frequency enables the inductance values for the inductors 83 and 88 (since the capacitors 84, 86 and 90 are all known to within close tolerances) to be easlly ascertainable. Impedance and time delay conditions are therefore also easily determined.

While the invention has been described in its preferred embodiments, it is to be understood that the words which have been used are words of description rather than of limitation and that changes Within the purview of the appended claims may be made without departing from the true scope and spirit of the invention in its broader aspects.

What is claimed is:

I. A tunable inductor comprising permeable means forming a magnetic path with an air gap therein, said means being of such geometry as to encompass an area of free space, a slug of permeable material adapted to be positioned within said air gap, and a coil of Wire so wound on said permeable means that at least part of a' turn of said coil surrounds said air gap, whatever of said turns are in said air gap being arranged to permit free movement of said slug in said gap, and the ends of said coil being substantially remotely located from said air gap.

2. A tunable inductor comprising a length of permeable material closed on itself to envelop substantially a particular area, the closure of said length of permeable material being such as to leave an air space between the two ends of said length, permeable means positionable within said air space, and an electric winding supported on said length surrounding said air space and extending from one side of said air space to the other side of said air space, but being disposed to permit positioning of said permeable means within said air space.

3. A tunable inductor comprising a ring of permeable material having a radially extending slot, a permeable slug adapted to be positioned within said slot, and a toroidal coil of wire so wound on the ring that turns of said coil at least partially envelop the slot, the ends of said coil being farther from said slot than the turns enveloping the slot.

4. A tunable inductor comprising a ring of magnetic material having a radially extending slot, means providing a sleeve in the interior of said ring, said sleeve being aligned radially with said slot, a slug of permeable material, stem means connected to said slug and slidable within said sleeve to move said slug relative to said slot, and a coil of wire so wound on said ring that at least part of one turn thereof bridges and surrounds the slot.

5. A tunable inductor comprising a ring of magnetic material having a radially extending triangular slot, means providing a sleeve in the interior of said ring, said sleeve being aligned radially with said slot, a slug of permeable material triangular-1y shaped to fit snugly with the sides of said slot, stem means connected to said slug and slid-able within said sleeve to move said slug relative to said slot, and a coil of wire so wound on said ring that at least part of one turn thereof bridges and surrounds the slot.

e. A network comprising a tunable inductor, two serially connected fixed capacitors connected in parallel with said inductor, and a series tuned circuit connected at.

the junction between said fixed capacitors, said tunable inductor comprising permeable means forming a magnetic path with an air gap therein, said means being or" such geometry as to encompass an area of free space, a slug of permeable material adapted to be positioned Within said air gap, and a coil of Wire so Wound on said permeable means that turns of said coil surrounds said air gap, said turns in said air gap being arranged to permit free movement of said slug in said gap, and the ends of said coil being substantially displaced from said air gap.

7. In a network having a parallel tuned circuit interconnected with a series tuned circuit, a tunable inductor in said parallel tuned circuit comprising a length of permeable material closed on itself to envelop substantially a particular area, the closure of said length of permeable material being such as to leave an air space between the two ends of said length, permeable means positionable References Cited by the Examiner UNITED STATES PATENTS 1,965,739 7/34 Galton 336l33 X 2,248,870 7/41 Fanger 336--133 2,411,370 11/46 Fries 336-l34 2,493,388 1/50 Candy 336133 X 2,791,752 5/57 Fredendall 333-75 ELI LIEBERMAN, Primary Examiner.

HERMAN KARL SAALBACH, Examiner. 

2. A TUNABLE INDUCTOR COMPRISING A LENGTH OF PERMEABLE MATERIAL CLOSED ON ITSELF TO ENVELOP SUBSTANTIALLY A PARTICULAR AREA, THE CLOSURE OF SAID LENGTH OF PERMEABLE MATERIAL BEING SUCH AS TO LEAVE AN AIR SPACE BETWEEN THE TWO ENDS OF SAID LENGTH, PERMEABLE MEANS POSITIONABLE WITHIN SAID AIR SPACE, AND AN ELECTRIC WINDING SUPPORTED ON SAID LENGTH SURROUNDING SAID AIR SPACE AND EXTENDING FROM ONE SIDE OF SAID AIR SPACE TO THE OTHER SIDE OF SAID AIR SPACE, BUT BEING DISPOSED TO PERMIT POSITIONING OF SAID PERMEABLE MEANS WITHIN SAID AIR SPACE. 